Lightning-protector.



W. DODD. LIGHTNING PROTECTOR..

APPLICATION man ocnzs, |911.

1,259,000. f Patented @121918.

WEST DODD, QF DES MOINES, IOWA.

LIGHTNING-PROTECTOR.

Speclcan'n of LettersvB-atent.

Application ledctober 23` 1-9'17.

'041%' 'whom #wLa-jl/ concern Be it known that I, VVes'r Dom), a citi-Zen ofthe United States, residing at Des Miei-nes, inthe county of Polk and State off Iowa, have invented certain new andx useful! Ilmprovements in- Li-ghtning- Protectors, of Whichthe following is a specifica-tion.

At the present time there are large n-um bers of" storage tanks for petroleum throughout the country, which tan-ks are constructed of metali bodyportions and wooden roofs. An alarming-ly lurge number of such petroleumstorage tanks are now being destroyed on account of electrical discharges usual-'ly occurring during thunder storms which cause sparks to pass between the wooden root` and the metal body a-nd ign-ite the vapors arising from the petroleum inthe tank.

The object of my inventionis toprovide means of Simple andf inexpensive construetion for collecting-and carrying off the static electrical charge from the wooden roof in suehamanner as to prevent the possibility of' the creation of sparks that might tend to ignite the sa-iclvapors'.

My invention consists in the construction, arrangement and combinationwith a- Wooden root of a charge collecting device locatedas closely as possible to that part ofv the roof adjacent to the top of the metal tan-k and in combining therewith suitable discharging devices arranged at intervals andi formingelectricalf conductors betweenthe collector ontheroof and: the bod-Iy.l of the metal tank :1s-.hereinafter more liullyset forth and illustratedf in the accompanying drawing, inwhich:

Figure l shows a vertical centralv sectional view of arnetal-lic tank and a wooden roof having my improvement appliedy thereto, and

Fig. 2 shows a detail sectional perspective view of a part of the top edge of the metal tank and5 a part ofv the wooden roofv havingmy improved charged collecting device applied to the roof and the discharging device communicating between said collecting device and the metal tank.

Referring to the accompanying drawing, I have used the reference numeral 10 to indicate the body portion of the metal tank. These tanks are usually made of metal sheets united at their edges by rivets. At the top edge is the usual outwardly extending fia-nge Patented Mar` 1,2, 1.913.

Serial No. 1198*,073.

formed integral with the top pla-tes and indicated' by the numerall 111.

The wooden roof is indicated by the reference numeral 12' and is-o the ordinary con` struction-- Its outer edge or periphery rests upon the metal flange-111'.

For the purpose of collecting an electric charge upon the wooden roof, I have provided' a collecting device preferablymade ofv copper cafble i-nd-i'cated generally by the nur-neral 13. rlhiscooper cable isplaced on the roof ata point as'cl'ose as may be praeticable to the edge ot"l the roof adjacent the metal flange 11f. In practice, I' usuallya-rrange this copper cable on the top surface ot the roo-f at the outeredge thereof. The copper cable ordinarily: has sufficient ilexibilityf tolie flatupon theroo-f and' to closelyfolllow' any irregularities inthe top: surface of the roo-t5 so. as to be inactual physical' con-tact with this top: surface of the root throughout its-entire length. completely surrou nding'theperiphery ofthe-root. I prelierably secure the collector cableto' thev noot at very: lire-quent intervals by nasa-ns.- of screws 113%- passed through the copper cable and: into. thewooden roei* tol thereby firmly hold thecopper-cable to its position in con-- tinuous: physical' contact with the roof sirrface- I have; inactual: practice provided additonal charge collecting' cables; These have been arrangedeoncentric with the; collection atv the periphery.l of the roof and spaced apart from it, such tor instance as: shown at 14.- i-n the draw-ing. This. inner cable or cables: as, the case may be, I electrically conneet tothe collector cable ati the periphery by radiallyarranged` collectons 1-5 electrifcally connected with the. several circular charge collectors..

I have provided for discharging the charge delivered to the collector cables as follows:

Secured to the collector cable at the periphery of the roof at suitable intervals are the discharging conductors 15a, the lower ends of which are electrically connected with the top edge of the metal tank. In practice, I usually accomplishl this by screwing copper or brass bolts 16 into the flange 11 and brazing the discharging cables into said copper or brass bolts 16 which are threaded and screwed in the flange. The

. narrow spaces which occur between discharging cables may be connected electrically and mechanically to the collecting cables by means of screws 17 assing through both cables where they overihp and into the Wooden roof.

During certain atmospheric conditions which occur during thunder storms, the metal tanks become heavily charged with electricity and at the same time, the wooden roofs become equally charged with electricity. The petroleum in the tanks is constantly giving olf vapor which is readily ignitible and this vapor is constantly discharging from the metal tanks through the the metal tank and the wooden roof so that an almost imperceptible electric spark passing between the wooden roof and the metal tank is sufficient at times to ignite the vapor and set fire to the petroleum in the tank resulting in the complete destruction of the tank, the cover and its contents. Many instances have occurred in which such tankswere ignited and burnt when the nearest lightning discharge was miles away from the tank. Vhen a lightning flash occurs within the area that is electrically affected by the lightnin Hash, the electric charge stored in a metallic tank that is within this area is instantly discharged into the earth, but the electric charge in the wooden roof cannot ass olf as rapidly as the charge contained 1n the metal tank due to the fact that the wooden roof itself is a poor conductor. This sudden discharge of the tank instantly creates a great difference in potential between the electric charge contained on the roof and that of the metal tank itself and at once sets up a condition in which the now free charge contained on the roof seeking to pass along the lines of least resistance to the metal tank arcs acrossthe spaces be* tween the roof and metal tank and thus forms sparks tending to ignite the vapors arising from the petroleum. By means of my improvement, I have provided means whereby the electric charge on the Wooden w Gopies n! this patent may be obtained for roof is prevented from arcing across the space between the wooden roof and themetal tank. It is only that part of the charge on the roof that is near the periphery of the roof that is likely to spark across the gap to the metal tank. By my improvement, the

charge collector that is arranged at the periphery of the roof and in close physical contact with the periphery of the roof causes all of the charge in its immediate neighbor` hood to enter the collector cable. This collector cable being made of copper and having high electrical conductivity, is of such nature that all of the charge collected by it will be instantly discharged to the metal tank without sparking at the instant the metal tank discharges to the ground.

It would be a matter of great difiiculty and great expense to electrically connect a wooden roof at' every point of its periphery with a metal tank. However, by my improvement, this is made unnecessary because of the fact thatI have provided a means for collecting all of the charge at the periphery of the roof into a copper cable and after the charge is thus collected, it may discharge into the metal tank through copper cables arranged at intervals` thus completely protecting the tank against the formation of sparks which might tend to ignite the vapors with a minimum amount of conductor cables that may be very conveniently and easily applied to the existing metal tanks with wooden roofs. I have found in actual practice that it is not convenient t'o place the collector cable 13 on the edge or periphery of the wooden roof. I therefore place it `on the relatively fiat top surface of the Wooden roof as near as possible to the edge andwhen this is done, I have found through laboratory experiments that a spark across the edge to the tank isvimpossible.

I claim as my invention:

The combination with a metallic storage tank, and a roof therefor having low electrical conductivity, of a collector ofstatic electricity from the roof comprising a metallic conductor extended completely around the roof at its periphery and in continuous physical contact with the roof, and a discharger for said collector comprising a series of conductors electrically connected with the collector and with the metallic tank.

In testimony whereof I afiix my signature in presence of two witnesses.

WEST DODD.

Witnesses: v

LUCY B. MCCARTHY, WALLACE A. DEANE.

ve cents each, by addressing the Commissioner o! Patents,

Washington, D. G. 

